Field of the Invention and Related Art Statement
The present invention relates to an oscillator having a temperature detecting faculty and a quartz vibrator for use in such an oscillator. The invention also relates to a method of measuring a temperature by using a quartz vibrator having the temperature sensing faculty.
There have been generally proposed the following two methods for stabilizing an oscillation frequency of a crystal oscillator. In a first method, the temperature of the quartz vibrator is maintained to be constant during the operation. A crystal oscillator whose frequency is stabilized by such a method is usually called a temperature controlled crystal oscillator. In a second temperature compensating method, the temperature of the atmosphere surrounding the quartz vibrator is detected and a load capacitance of the quartz vibrator is changed in accordance with the detected temperature of the ambient atmosphere. A crystal oscillator whose oscillation frequency is compensated for by the second method is generally called a temperature compensated crystal oscillator.
In the former temperature controlled crystal oscillator, the quartz vibrator is placed in a source of heating and cooling which is controlled by a thermostat and is kept at a desired temperature. When a cutting angle of quartz is suitably selected, the temperature characteristic of the oscillation frequency of the quartz vibrator becomes substantially flat in a temperature range of 60.degree. to 70.degree. C., so that the operating temperature of the quartz vibrator is usually set at a temperature within said range. Since the operating temperature is higher than the room temperature, the thermostat usually comprises a heater, but does not include a cooling device or element. That is to say, the temperature of the thermostat is measured by a thermistor and the heater is selectively operated in accordance with a deviation of the thermostat temperature from a standard temperature. In the temperature compensated crystal oscillator, the ambient temperature is measured by a temperature detecting element such as the thermistor and the load capacitance of the oscillator is controlled in accordance with a deviation of the detected temperature from a standard temperature.
In the known temperature controlled crystal oscillator mentioned above, the thermistor is used as the temperature detecting element. However, the material, shape and size of the thermistor are entirely different from those of the quartz vibrator, so that the temperature variation of the thermistor does not accurately reflect the temperature variation of the quartz vibrator. Therefore, it is very difficult to maintain the temperature of the quartz vibrator at the desired constant temperature. In other words, although the temperature of the thermostat is controlled on the basis of the detected temperature, the quartz vibrator is not kept at the desired temperature, so that the oscillation frequency deviates from a desired frequency. In order to avoid the above mentioned drawback, the construction and mutual position of the quartz vibrator and thermistor have to be changed. But in practice, it is rather difficult to attain the optimum design, and thus the oscillation frequency of the quartz vibrator could not be maintained at the desired frequency in an accurate and reliable manner.
In the temperature compensated crystal oscillator, the thermistor is also used for measuring the ambient temperature, so that the above explained drawback could not be avoided.
It has been known that a specially cut quartz vibrator has the temperature characteristic in which the oscillation frequency is varied at a rate of several ppm per a unit temperature variation of 1.degree. C. Then it has been proposed to detect the temperature of the quartz vibrator by measuring the temperature of the quartz vibrator and the oscillation frequency is controlled in accordance with the detected temperature. However, since the frequency variation is very small, it is practically impossible to detect it precisely. Due to this, this compensating method has not been actually used.